The injectors of internal combustion engines have tolerances which can lead to unexpected inaccuracies with regard to the injected fuel amount and which can thus result in an impairment in the quality of the emissions of the internal combustion engine. This can be prevented by means of an adaptation of the injector characteristic over the operating duration of the internal combustion engine. It is known for the characteristics of injectors in gasoline and diesel engines to be adapted over the operating duration of the engines in order to compensate for production tolerances and changes occurring during operation. The adapted injector characteristics are then used for the further control of the injectors, such that exact fuel amounts can be injected.
It is thus possible, by means of an exact adaptation of the overall injector characteristic, for even injectors with a high tolerance drift over their service life to be used to adhere to even more stringent future emissions requirements.
To perform such an adaptation of the injector characteristics, it has hitherto been the case that, during fuel shut-off phases, test injections were carried out in which periodic injection pulses for one of the injectors were carried out in order to inject a small amount of fuel, for example every second time a top dead center of the corresponding cylinder was reached (in-house prior art). During said test injections, the rotational speed behavior of the internal combustion engine was observed by means of the crankshaft position sensor. From the rotational speed behavior, the generated engine torque was estimated and the corresponding fuel amount to be injected was calculated. By carrying out said process repeatedly for each cylinder, it was possible for the injector parameters for each cylinder to be adapted during the operation of the internal combustion engine.
With said adaptation method, however, rotational speed oscillations of the internal combustion engine can arise, which have a disturbing effect. The method therefore has only a limited scope for use, and in particular can be used only in conjunction with small fuel amounts and only in conjunction with certain drive situations. Furthermore, considerable calibration outlay is required for the estimation of the generated torque from the determined rotational speed.
A method having the features of the preamble of patent claim 1 is known from DE 103 05 523 A1.
It is known from EP 0 899 151 A2 to re-establish the functionality of a NOx adsorption device by means of enrichment, and to compensate the resulting torque pulses by means of the regenerative braking force of an electric motor.
It is known from DE 10 2006 013 295 A1 for changes in torque of an internal combustion engine owing to switching between operating modes to be compensated by means of an electric motor.
It is described in DE 197 51 100 A1 that torque fluctuations of an internal combustion engine are suppressed by changing the current of an electric motor on the basis of a value determined by a torque/motor current characteristic curve decision device.
With the known adaptation methods, it is however only possible to adapt the injector characteristic in the case of very small injection amounts.